Installation and method for manufacture of an optical fiber cable

ABSTRACT

An optical fiber cable, including optical fibers and a tube housing the fibers, is made by a process wherein optical fibers are fed from one or more pay-out device to the interior of an extrusion head which also receives a sheathing material in viscous form. The extrusion head extrudes the viscous material to form a sheath surrounding, but out of contact with the fibers. With the fibers still out of contact with the sheath, the fibers and sheath pass through a jig which calibrates the sheath to the final form of the tube, and cools the viscous material in a first stage of solidification. Thereafter, the cable comprising the tube and optical fibers is would up around a first draw-in device and heat treated. From the first draw-in device the cable passes to a second draw-in device with the tension of the cable between the two draw-in devices being regulated.

FIELD OF THE INVENTION

The present invention concerns a method as well as an installation forthe manufacture of an optical fiber cable.

BACKGROUND OF THE INVENTION

Known optical fiber cables include a bundle of fibers assembled togetherin the form of layers, of already cabled fibers or of strips which aresurrounded by a first outer tube of rigid or flexible structure formedby extrusion of a synthetic material.

In certain applications, optical fibers are housed in a loose manner onthe interior of the tube and a viscous material such as a protectiongrease known under the British name "jelly" is injected into theinterior of the tube in order to embed said fibers in the latter.

The manufacture of this type of cable is brought about in a manner suchthat the fibers on the interior of the tube exhibit relative thereto aselected excessive length obtained by the influence and the combinationof different parameters throughout the entire manufacturing chain.

In the known methods and installations presently used, the opticalfibers are unwound from a pay-out device including a feed reel freelymounted in rotation on an axle, the tension of the unwound fiber beingcontrolled so as to remain constant.

Such fiber is thereafter drawn down through an extrusion head in whichsynthetic material at a high temperature in a viscous form is suppliedaround said fibers in order to form the protection tube hereinbeforementioned in a manner coaxial to and on the exterior of the fibers.

At this point, the grease or "jelly" is injected in order to fill thetube and for coating the optical fibers in the latter.

After this extrusion step, the plastic tube is cooled in a first coolingreceiver and is urged in traction in being wound around a first draw-inreel. The method is continued by the passage of the tube through anothercooling receiver and through another draw-in reel with a control of thetractions on such tube through the use of strain gauges.

Such method and installation give satisfaction but solely up to a limitdiameter of the tube and up to a limited number of fibers on theinterior of the tube. Effectively, and in particular, beyond a tubediameter of 6 mm, the appearance of defects is ascertained in the outerform of the tube, but also in the excess length of the fibers as well asin the aspect of its outer surface. Is is thus very difficult to obtaina tube exhibiting a smooth outer surface and the excessive length alsobecomes difficult to control.

SUMMARY OF THE INVENTION

An object, the present invention is to provide a method and aninstallation for the manufacture of an optical fiber cable enabling theovercoming of such drawbacks and thanks to which the smooth aspect andthe circular form of the tube surrounding the fibers can be controlled,whatever be the number of fibers on the interior of the latter,whilstmoreover enabling a sufficient control of the excess length on suchfibers.

A object of the invention is to provide a method of manufacture of anoptical fiber cable including a tube in which said fibers are housed,characterized in that it includes the following steps in which:

a) optical fibers are brought from one or several pay-out devices,

b) such fibers are introduced into the interior of an extrusion headsupplying a sheathing material in viscous form extruded from said headaround the fibers,

c) at the output of the extrusion head, the sheathing material isdirectly preformed so as to cause it to take its definitive geometricform corresponding to that of the solid tube before and while itenvelops said fibers,

d) the cable made up from the tube and fibers is rolled up around afirst drawn-in reel, then

e) the cable is cooled in order next to cause it to pass through asecond draw-in reel, while maintaining constant the tension between thetwo draw-in reels.

A further object of the invention is provided an installation for themanufacture of an optical fiber cable comprising:

pay-out means capable of supplying optical fibers, for example under theform of ribbon, and

extrusion means of a sheathing material arranged after the pay-out meansand through which said fibers are brought, characterized in that itfurther includes calibrating means for the sheathing material, suchmeans which are arranged following the extrusion means, being capable ofmaintaining the sheathing material in a preformed form corresponding insolid form to the definitive geometric form of a tube intended tosurround the fibers and this before and while the material envelops saidfibers.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, characteristics and advantages of the invention willappear upon reading of the detailed description which follows preparedhaving reference to the attached drawings which are given solely bywayof example and in which:

FIG. 1 is a schematic view and an elevation of an installation formanufacture of an optical fiber cable according to the invention;

FIG. 2 is a longitudinal cross-section view of an extrusion head and ajig of the installation of FIG. 1, and

FIGS. 3a and 3b are transverse cross-section views of two optical fibercables obtained by the method and the installation according to theinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In referring initially to FIGS. 3a and 3b, there will be describedhereinafter two optical fiber cables according to two embodimentsobtained by the method and by the installation according to theinvention, which will be described in a more detailed fashionhereinafter.

Such cables, which are here identified by the general reference 1, eachcomprise an outer tube 2 formed of a flexible or preferably rigidsynthetic material such as polyamide, polybutylene terephthalate orpolypropylene. On the interior of tube 2 which, as is seen on FIG. 3,exhibits a circular form in cross-section, are housed a certain numberof optical fibers 4 (a single one being here referenced) assembledtogether in the form of sheets or strips 6a according to the embodimentof FIG. 3a. As is seen on such figure, the layers or strips 6a aremaintained relative to the outer tube 2 at a radial distance d from thelatter, so that the layers or strips 6a do not touch the inner wall ofthe tube 2.

In conformity with the embodiment of FIG. 3b, the optical fibers 4 areamalgamated among themselves in four bundles or cables 6b respectivelymaintained and surrounded by a retention tube 3. Each bundle 6b and inparticular its retention tube 3 is arranged at a distance d from theouter tube 2 in which is injected the grease or "jelly" V. Theinvention, as is well understood, is not limited to the obtaining ofcables according to FIGS. 3a and 3b which are shown here by way ofexample.

A viscous material V, such as a protection grease, generally known underthe British name "jelly", is injected into the interior of tube 2 inorder to fill the free space left between the tube 2 and the opticalfiber layers or strips referenced 6a or the cabled bundles 6b.

In referring henceforth to FIG. 1, there will be described hereinafteran installation for the manufacture of the cable 1 in conformity withthe invention, such installation being identified by the generalreference 10.

In the rest of the description, the terms "upstream" and "downstream"will be used with reference to the sense of running of the opticalfibers 4 and more generally with reference to the sense of running ofcable 1 in the installation 10 in conformity with arrow D.

Furthermore, the term "optical fibers" accompanied by reference 4, willbe used to qualify generally fibers in the form of strips referenced 6aor the form of already sheathed bundles referenced 6b, and this in orderto facilitate the rest of the description.

At its upstream portion, installation 10 is provided with pay-out means12 which include several feed reels (not shown) on which the opticalfibers 4 are rolled.

The optical fibers 4 which are shown in a schematic manner on FIG. 1 byan interrupted dash-and-dot line, are drawn from the pay-out means 12 inorder to pass through an extrusion head 14 shown in a more detailedmanner on FIG. 2. Such extrusion head 14 which is basically of knownstructure is capable of carrying under fusion a synthetic material,generally supplied in granulated or compounded form, by heating to veryhigh temperatures.

At the output of the extrusion head 14, the material (referenced M onFIG. 2) which is delivered in the viscous state and at very hightemperatures (fusion temperature) is forced into displacement underpressure in the downstream direction around an extrusion die N whichgives the material M the form of a hollow envelope.

This viscous form of the material M obtained at the output of theextrusion head 14 at the level of the die N, is identified on FIG. 2 bythe reference FV.

Downstream of the extrusion head 14 is arranged a jig 16 in which areintroduced the fibers 4 which have previously traversed the extrusionhead in the form of layers, of strips or of sleeved bundles, as well asthe sheathing material M in its viscous form FV in a manner coaxial tothe latter..

In a preferred embodiment of the invention, there is also introducedinto jig 16 the protection grease V intended to fill the tube 2.

Reference will be carried over henceforth to FIG. 2 which shows, in amore detailed manner, the extrusion head 14 as well as the entry of thejig 16.

On such figure, the optical fibers 4 have likewise been shown in aschematic manner by an interrupted dot-and-dash line.

The extrusion head 14 being of basically standard conception will not behere described in a detailed manner.

It is simply specified that the optical fibers 4 are introduced frombehind into the extrusion head 14 through a tubular guide 18 whichadvances up to the level of the die N around which arrives the materialM, in its viscous form FV.

As is see on such figure, the optical fibers 4 next pass through the jig16 and penetrate further ahead into a part of the latter which is shownon such figure in a partial and very schematic manner.

Jig 16 includes two chambers 20 and 22 in which a fluid such as watercirculates at a temperature T1 on the order of 10° to 50° C. Morespecifically, such temperature is maintained between 15° and 25° C. andcan, in certain cases, be brought to 40° C.

Jig 16 which is also known under the name of calibration receiver is initself of known conception and also will not be further here describedin a very detailed manner.

It will simply be mentioned that the circulation of water in theinterior of chambers 20 and 22 (circulation which is permitted by avacuum pump of the water ring pump type, not shown) causes a partialvacuum to appear on the interior of chamber 22, but under a controlledtemperature. Such cooling temperature assures a first stage ofsolidification of the extruded synthetic material M.

Jig 16 includes a calibration socket 24 against which the material M isapplied by suction thanks to the vacuum phenomenon mentionedhereinabove, such material M which is thus found to be preformed by themechanical and thermal actions of the jig 16 thereby assuming a solidform referenced FS, corresponding to the definitive geometric form ofthe tube referred to as the solid tube, referenced 2 on FIG. 3.

It will be further noted that the extrusion die N includes a feed neck26 which is arranged in a manner coaxial to the tubular guide 18 and inwhich circulates at least the optical fibers 4. In a variant of thepreferred embodiment, the protection grease or "jelly" V (FIG. 3) isalso caused to circulate on the interior of the feed neck 26.

The feed neck 26 physically isolates the optical fibers 4 as well as thegrease V from all contact with the sheathing material M, at least overan introduction distance of the sheathing material M into the interiorof the calibration socket 24 on jig 16, such distance being sufficientlygreat to enable the preforming of the tube 2 by solidification ofmaterial M, prior to any contact of such material with the fibers 4 andthe protection grease V.

In effect it will be noted on FIG. 2 that the feed neck 26 penetrates ina coaxial manner into the interior of the calibration socket 24 as wellas into the first cooling ring formed by chamber 20. Thereby, thematerial M, before entering into jig 16 is already interiorly guided bythe feed neck 26 of the extrusion die N and begins its solidification ina progressive manner by the cooling due to the action of the watervaporized at temperature T1 in chambers 20 and 22.

Material M having begun its solidification, is held in this form, thatis to say preformed, by the cooling ring, against the calibration socket24 which leads progressively to the formation of the tube 2 of FIG. 3.

In the variant embodiment shown, the protection grease or "jelly" isinjected into the interior of tube 2 via the feed neck 26.

To this end, as is seen on FIG. 2, the installation according to theinvention includes, in a manner coaxial to the tubular guide 18, aperipheral chamber 28 for feeding the protection grease (here not shown)which is introduced by a back connection coupled to a pipe, itselfconnected to a receptacle or container (not shown). The protectiongrease is thus forced to circulate in the annular chamber 28 coaxial tothe optical fibers 4 up to a mixing chamber 32 formed in the feed neck26.

It is thus noted that the assembly "protection grease-optical fibers"comes into contact with material M only when such material has beenintroduced into the jig 16, and more specifically following itsintroduction into the interior of the calibration socket 24.

Here it will be noted that the protection grease of "jelly" can bebrought to a temperature on the order of 30° to 250° C. according to theexcess length which is desired on the optical fibers 4.

It will thus be understood from what has just been described that therehas been provided an installation including downstream of the pay-outreels 12, extrusion means 14 for the feeding material M as well ascalibration means 16, 24 for such material, which are themselvesarranged downstream of the extrusion means 14. It will be understoodthat in this arrangement the calibration means 16, 24 are capable ofmaintaining the sheathing material in a preformed form corresponding tothe definitive geometric form of tube 2 once it is solid, and thisbefore and while the material M envelops the fibers 4 and the protectiongrease V.

In referring henceforth to FIG. 1, there will be described the differentunits of the installation 10 according to the invention arrangeddownstream of the jig 16. Thus, following jig 16 is arranged a firstreceiver 40 at a controlled temperature in which circulates a liquid ata temperature T2 greater than or equal to the temperature T1 of jig 16.

Downstream of such first receiver 40, there is arranged a main drawn-inreel 42 which is formed by wheel 43 of large diameter (on the order of600 to 2500 mm). Within the draw-in reel 42, which forms a verticalreheat receiver, a temperature T3 greater than the temperature T2 ismaintained, chosen as a function of the excess length desired on theoptical fibers 4.

Next, downstream of such main draw-in reel 40, there is arranged asecond cooling receiver 44 maintained at a temperature T4 generallylower than temperatures T2 and T3.

The installation 10 further includes a secondary draw-in reel 46arranged substantially at the end of the manufacturing chain.Furthermore, a tension regulator 48 is arranged between the principaldraw-in reel 42 and the secondary draw-in reel 46 in order to assure acontrolled tension of cable 1 between the two draw-in reels 42 and 46.

Thus, it is understood that there has been provided a manufacturingmethod and installation for an optical fiber cable in which the materialM intended to form tube 2 surrounding the optical fibers 4, entersimmediately under its viscous form FV into the jig 16 so as to bedirectly preformed at the output of the extrusion head 14 and to assumethe definitive geometric form of the tube in its solid form before andwhile the optical fibers 4 and the protection grease or "jelly" Vpenetrates into the interior of tube 2. Furthermore, it is ascertainedthat the material M is preformed in cooling it to the temperature T1,which temperature is provided thanks to a supply of cold water to jig16. Furthermore, after the sheathing material M intended to constitutetube 2 has been preformed in jig 16, the sleeved cable 1 is introducedinto the receiver 40, the controlled temperature of which is maintainedat a temperature T2 greater than or equal to the temperature T1 in orderthat the tube 2 be reheated once it has left the jig 16.

I claim:
 1. A method of manufacture of an optical fiber cable including a solid tube in which said fibers are housed, comprising the following steps, in which:a) optical fibers are brought from at least one pay-out reel, b) the optical fibers are introduced into the interior of an extrusion head while supplying a sheathing material around the fibers so as to constitute a hollow envelope extruded in viscous form, c) directly from the output of the extrusion head the fibers and the extruded hollow envelope are introduced into the interior of a jig which cools the material to a temperature T1 and which guides the cross section of the hollow extruded envelope so as to bring it to a stage of solidification while causing it by calibration to assume its final form, corresponding to that of the solid tube before and while such sheathing material envelops said fibers, d) the cable made up from the tube and fibers is rolled up around a first draw-in reel, then e) the cable is cooled, and, f) thereafter the cable is passed through a second draw-in reel while maintaining constant the tension between the two draw-in reels.
 2. A method as set forth in claim 1, wherein protection grease is injected into the interior of the tube after the material forming the hollow extruded envelope has been introduced into the jig.
 3. A method as set forth in claim 1, wherein the sheathing material is calibrated by causing it to pass through a jig under vacuum which applies the material by exterior suction against a calibration socket exhibiting a predetermined diameter, corresponding to the final form of the tube.
 4. A method as set forth in claim 1, wherein the cable is heated following its exit from the jig until its exit from the first draw-in reel.
 5. A method as set forth in claim 1, wherein temperature T1 is between 10° and 40° C.
 6. A method as set forth in claim 3, wherein the sheathing material is cooled by the circulation of a cooling liquid at the temperature T1 through the socket of the jig.
 7. A method as claimed in claim 1 wherein the cable, following its exit from the jig to its exit from the first draw-in reel, is maintained at a temperature T2 which is at least equal to the temperature T1, and is heated to a temperature T3 which is greater than the temperature T2.
 8. A method as set forth in claim 7, wherein the sheathed cable at the output of the jig is introduced into a container at a controlled temperature maintained at temperature T2.
 9. A method as set forth in claim 7, wherein the first draw-in reel is maintained at temperature T3 which is greater than temperatures T1 and T2.
 10. An installation for the manufacture of an optical fiber cable including a solid tube in which optical fibers are housed, comprising:pay-out means for supplying optical fibers, and, extrusion means arranged following the pay-out means through which said fibers are led, such extrusion means supplying a sheathing material around the fibers constituting a hollow extruded envelope in viscous form, and including a jig arranged following the extrusion means, such jig cooling the extruded material to a temperature T1 in guiding the cross section of the hollow extruded envelope so as to bring it to a stage of solidification while causing it by calibration to assume its final form, corresponding to that of the solid tube, before and while such sheathing material envelops said fibers.
 11. An installation as set forth in claim 10, wherein the jig includes a calibration socket arranged at the output of the extrusion means.
 12. An installation as set forth in claim 11, wherein the jig is under vacuum so as to be capable of applying by the exterior the sheathing material at the output of the extrusion means against the calibration socket.
 13. An installation as set forth in claim 11, further including an arrangement for putting a cooling liquid into circulation in the interior of the jig around the calibration socket.
 14. An installation as set forth in claim 11, including a feed neck intended to bring the fibers and a protecting grease having to fill the tube to the output of the extrusion means, such feed neck, which penetrates to the interior of the calibration socket, maintaining the sheathing material isolated at the same time from the fibers and said protecting grease at the time of entry of the material into the calibration socket so as to avoid all contact of such material with the fibers and the grease before the cooling of said material.
 15. A method of manufacturing an optical fiber cable, said method comprising the steps of:feeding optical fibers from at least one pay-out reel to an extrusion head; supplying a sheathing material to the extrusion head; extruding the sheathing material from the extrusion head to form a tube with the optical fibers enclosed in said tube, the optical fibers being maintained out of contact with the tube during the extruding; while said optical fibers are still maintained out of contact with the tube, feeding the tube with the optical fibers therein through a jig to calibrate the tube to its final form, and, bringing the calibrated tube to a stage of solidification while still maintaining the optical fibers out of contact with the tube.
 16. A method as set forth in claim 15, wherein protection grease is injected into the interior of the tube after the material forming the tube has been introduced into the jig.
 17. A method as set forth in claim 15, wherein the sheathing material is calibrated by causing it to pass through a jig under vacuum which applies the material by exterior suction against a calibration socket exhibiting a predetermined diameter, corresponding to the final form of the tube. 